The present invention relates to a process for continuous preparation of filament-like polymer crystals from a solution of a crystallizable polymer, such as polyethylene and polypropylene, wherein a seed crystal grows longitudinally in the flowing solution and the grown polymer filament thus produced is removed from the polymer solution at an average rate which is equal to the growth rate.
In the publication Colloid and Polymer Sci. 253, 452-461 (1975), by Zwijnenburg, A. and Pennings, A. J., the formation of filament like polyethylene crystals from a xylene solution thereof in a Poiseuille flow is described. At the beginning of a capillary, through which flows an undercooled solution of polyethylene is xylene, a polyethylene seed crystal is suspended in said polyethylene solution. Then, by winding the longitudinally growing crystal on a reel at a rate which is equal to the growth rate, an endless filament-like polymer crystal can be prepared. This technique resembles that of Czochrakshi as described in Phys. Chem. 92, 219 (1918) for the growth of single crystals of metals and inorganic substances, the difference of course, being that the growing polymer crystal forms from a solution which is subject to a Poiseuille flow. It was thought then that the growth rate was determined by the quantity of polymer solution that flowed past the seed crystal.
Although the mechanical properties of the filaments according to the Zwijnenburg et al process are extraordinarily good, the longitudinal growth rate is much too small for the process to be of industrial significance. The object of the present invention, therefore, is to provide a process and apparatus in which a considerably greater growth rate of the crystals is obtained.
Another object of the present invention is to provide filaments having extraordinarily good mechanical properties.
Further objects of the invention will appear from the following specification, drawing and examples.